io_uring: don't cancel all work on process exit

to #26323578

commit ebe10026210f9ea740b9a050ee84a166690fddde upstream.

If we're sharing the ring across forks, then one process exiting means
that we cancel ALL work and prevent future work. This is overly
restrictive. As long as we cancel the work associated with the files
from the current task, it's safe to let others persist. Normal fd close
on exit will still wait (and cancel) pending work.

Fixes: fcb323cc53e2 ("io_uring: io_uring: add support for async work inheriting files")
Reported-by: NAndres Freund <andres@anarazel.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io_uring.c

@@ -5031,10 +5031,6 @@ static int io_uring_flush(struct file *file, void *data)
 	struct io_ring_ctx *ctx = file->private_data;
 
 	io_uring_cancel_files(ctx, data);
-	if (fatal_signal_pending(current) || (current->flags & PF_EXITING)) {
-		io_cqring_overflow_flush(ctx, true);
-		io_wq_cancel_all(ctx->io_wq);
-	}
 	return 0;
 }